Electronic tube structure



March 17, 1959 w. T. MlLLlS ELECTRONIC TUBE STRUCTURE Filed Nov. 9, 1954 EMISSIVE COATING BASE MATERIAL MEMBER EMISSIVE COATING BASE MATERIAL EMISSIVE m s l- U Rll mM Me T um l F- T T VR I m mm c S E A H w w s M E Y B 4 COATING United States Patent ELECTRONIC TUBE STRUCTURE Walter Townsend Millis, Owensboro, Ky., assignor to General Electric Company, a corporation of New York Application November 9, 1954, Serial No. 467,837

9 Claims. (Cl. 313-346) My invention relates to electronic tubes and pertains more particularly to a new and improved low-microphonics tube including a new and improved 'low expansion cathode.

'In some electronic tubes such as the receiving tube types, indirectly heated cathodes are employed. Often these cathodes comprise a metallic sleeve having an electron emissive substance coated on the exterior thereof.

The sleeve is adapted for containing a filament which when energized is effective for heating the sleeve to render the coating thereon emissive. Heretofore, it has been found that certain materials are more desirable than others in forming the cathode sleeve, since such materials provide a more suitable base for the electron emissive coating. Substantially pure nickel, and certain nickel alloys, for example, have been found to be very suitable base materials for the emissive coating and, consequently, have been widely employed for forming cathode sleeves. Unfortunately, however, these materials are What might be characterized as high thermal expansion and high heat conductivity metals and when used in the formation "of cathode base members result in several disadvantages. For instance, cathode sleeves are usually supported in a tube cage structure by having the ends thereof extend through suitable apertures in spaced insulative supports such as mica disks. Now, it is desirable from the standpoint of microphonics to have the sleeve ends fit tightly in the apertures in the mica disks. There is, however, a limitation as to how tight this fit may be, owing to the fact that during the operation of the tube the cathode expansion resulting from the heating thereof will, if the sleeves are tightly fitted in the mica disks, cause the sleeves to bow outwardly intermediate the disks and thereby cause inconsistent spacing between the sleeve walls and other tube electrodes. Additionally,

circumferential expansion of the ends of the sleeves in the support apertures will, if the 'fit is tight, expand the apertures or result in a crimping of the sleeve ends. These effects will subsequently result in a looseness of the fit and cause microphonics.

Another undesirable effect experienced with cathode sleeves formed of nickel and other high thermal expansion materials which are noted for their suitability in forming the base members of cathode structures, is the loss of heat through the insulative supports. That is, these materials, since they have a high thermal conductivity, readily conduct heat to the mica supports which causes higher axial cathode temperature gradients and reduced thermal efficiencies. Additionally, these materials generally do not have a desired high degree of strength at high temperatures.

Accordingly, the primary object of my invention is to provide a low-microphonics electronic tube.

Another object of my invention 'is to provide a new and improved cathode structure.

Another object of my invention is to provide a low expansion cathode structure.

Another objectof myinvention is to provide a low 'ex- 2,878,410 Patented Mar. 17, 1959 hi pansion cathode structure including a surface portion adapted for serving suitably as a base for an electron emissive material coating.

Another object of my invention is to provide a new and improved electron tube device having a cathode structure adapted for being tightly fitted in support members therefor, for the purpose of minimizing microphonics.

Another object of my invention is to provide a new and improved cathode structure adapted for minimizing axial cathode temperature gradients and increasing the thermal efliciency thereof.

Still another object of my invention is to provide a new and improved cathode structure which will have high strength at elevated temperatures.

Further objects and advantages of my invention will become apparent as the following description proceeds and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming part of this specification.

in carrying out the objects of my invention 1 provide an electronic tube including a cathode structure tightly fitted in supports in the tube and comprising a member formed of a low thermal expansion and low heat conductivity material, an electron emissive coating and a layer of material interposed between the member and the emisslve coating and formed of a material suitable for serving as a base for the emissive coating. The interposed layer is of such thinness relative to the member as, to result in no appreciable thermally caused mechanical distortion owing to a thermal bimetal effect. Additionally, the absence of a bimetal effect may be insured by providing a layer of material, similar to that interposed between the one surface of the base member and the electron emissive coating, on the opposing surface of the base member.

For a better understanding of my invention reference may be had to the accompanying drawing in which:

Fig. l is an enlarged fragmentary partially sectionalized view of an electronic tube constructed in accordance with my invention;

Fig. 2 is an enlarged fragmentary partially sectionalized View illustrating a form of my new and improved low expansion cathode; and

Fig. 3 is an enlarged fragmentary detail illustrating a modified form of my cathode.

Referring to Fig. 1, there is fragmentarily shown an electronic tube generally designated 1 and including a bulb 2 formed of glass or any other suitable insulative material. The bulb 2 houses an assembly of electrical elements generally referred to as a tube cage structure and designated 3.

The tube cage 3 includes a spaced pair of insulative members 4 for supporting the various other elements of the cage. Preferably, the members comprise mica disks formed to include suitable apertures for receiving the ends of, and thereby supporting, the other elements therebetween. For instance, the cage structure 3 may include a tubular plate or anode 5 formed to include a plurality of tabs 6 spaced about the ends thereof. The tabs may be adapted for extending through suitable apertures in the disks 4 and then being bent, thereby to secure the plate between the disks. Additionally, the cage may include a grid '7 which may be formed by securing a helically wound grid wire 8 a spaced pair of vertical grid support rods 9. In such a structure the grid 7 is supported between the disks. 4 by end portions 10013 the grid support rods extending through suitable apertures in the disks 4.

Still further the cage structure may include a cathode 13 comprising a base member coated with a suitableelectron emissive material such as barium oxide. .As shown,

nected to conductors which extend in a sealed manner through the lower end of the bulb 2, thereby to provide for electrical connections to these elements. It is to be understood that the triode shown in Fig. 1 is intended merely to be illustrative of the general type of tube structures to which my invention is applicable, and that my invention is equally applicable to tubes having various numbers of electrodes.

Now, as pointed out above, it has heretofore been the practice of forming the base members of cathodes such as 13 of nickel, nickel alloys and other materials suitable for serving as bases for electron emissive coatings. As also pointed out above, these materials, while suitable as bases for the coatings are generally high thermal expansion and high heat conductivity materials. As a result, cathode base members formed of these materials tend to expand considerably when heated during operation of the tubes. Also, the high heat conductivity of these materials results in considerable heat loss to members in contact therewith. Such high expansion and heat loss in cathodes results in various operational disadvantages. For instance, as seen in Fig. 1 and as pointed out above, the cathode 13 is adapted for being supported in the cage structure by having the end portions thereof extend through suitable apertures in the spaced mica disk supports 4. In order to minimize microphonics, it is desirable that the ends of the cathode 13 fit tightly in the apertures in the mica disks. When nickel, nickel alloys or other materials having high thermal expansion are utilized in fabricating the cathode base members, however, a tight fit such as that desired results in restraint of the ends of the cathodes and bellying or outward bowing of the intermediate portions thereof due to the high thermal expansion of the members. This outward bowing results in inconsistent spacing between the electron emissive coating and the grid and plate, which is operationally undesirable. Additionally, the end portions of the cathodes in the apertures tend to expand circumferentially when the cathodes are heated which causes either enlargement of the apertures or crimping of the cathode ends, both. of which conditions tend to loosen the fit of the cathodes in the disk apertures and thereby result in microphonics. Still further, the high thermal conductivity of nickel and nickel alloys results in the high heat loss from the cathodes to the mica disks which, in turn, causes higher axial cathode temperature gradients and reduces the thermal efficiencies of the cathodes.

My invention contemplates the provision of a low expansion low axial thermal conductivity cathode including a suitable base surface for an electron emissive coating thereon. As seen in Fig. 2, a cathode l3 constructed in accordance with my invention may comprise a tubular or otherwise configured base member 15 formed of a suitable low expansion low thermal conductivity material such as Invar, Nilvar, Kovar, Rodar, or any similar low thermal expansion and conductivity metal.

Invar and Nilvar are low thermal expansion, low thermal conductivity materials available through the Carpenter Steel Company and the Driver-Harris Company, respectively, and each, according to standard handbooks of metallurgy has the following percentage composition:

Sulphur .04 maximum. Phosphorus .03 maximum. Iron Remainder.

Kovar is another low thermal expansion, low thermal conductivity alloy. It is available through the Stupakotf Ceramic and Manufacturing Company and, according to standard metallurgy handbooks, has the following percentage composition:

Iron 53 -54.

Nickel 28.529.5. Cobalt 16.5-17.5. Manganese .5 maximum. Silicon .2 maximum.

Carbon .06 maximum.

Nickel 29 Cobalt 17 Manganese 30 Ir Remainder Invar, Nilvar, Kovar and Rodar, in addition to being low thermal expansion and low thermal conductivity materials are further suitable for use in forming my cathode base member 15 in that they have high strength at elevated temperatures.

Provided on, and suitably secured to the surface of the low expansion base member 15 so as to provide good heat transfer, is a layer of material 16 suitable for serving as a base for an electron emissive material coating 17. Substantially pure nickel, platinum-iridium, nickel alloys, such as nickel-cobalt, nickel-cobalt-titanium, nickelcobalt-manganese, all in various percentages, and various other materials have heretofore been found to serve suitably as a base for electron emissive materials in manufacturing cathode structures. Accordingly, the layer 16 may be formed of nickel or any of the nickel alloys or other materials which are suitable as electron emissive material bases.

Now, as brought out above, nickel, nickel alloys, and other materials which have heretofore been found to serve well as bases for electron emissive materials are high thermal expansion and conductivity materials and for this reason they generally have not been found fully satisfactory for forming cathode base members. Owing to the high thermal expansion characteristic of these base materials, I have formed the layer 16 thereof to be so thin relative to the wall of the base member 15 as to minimize any thermally caused mechanical distortion that might tend to result in the structure owing to differences in coefficients of expansion of the base member and the layer of emissive coating base material. In other words, there is no appreciable thermal bimetal effect in the structure. I have found that the optimum relative thicknesses of the layer 16 and the wall of the low expansion cathode base member 15 to be approximately 1 to 6. It has been my experience that with such relative dimensions, the layer 16 is adequate as a base surface for the electron emissive material coating 17 and is sutficiently thin as to have no appreciable bimetal effect on the structure as a whole.

With my invention the ends of the cathode 13 may be tightly fitted into the apertures in the support micas 4 during assembly of the cage structure 3 without resulting in the heretofore experienced disadvantages encountered with the use of the cathode base members formed wholly of nickel and other high expansion materials, i. e., when my cathode 13 is heated during operation there is no appreciable longitudinal expansion of the base member 15 with the result that there is no appreciable outward bowing of the portion of the cathode intermediate the mica disks 4 or circumferential expansion of the end portions of the cathode in the apertures in the micas. As a result,

the spacings between thecathode and grid and plate remain substantially .constant and the mica apertures are not enlarged nor are the cathode ends crimped. The tight fit of the cathode ends in the mica apertures obtained during assembly is retainedithroughout the life of the tube and no microphonics owing to a loose fit result.

As pointed out above, it is desirable that the layer of material 16, provided on the surface of the base member and interposed between the base member and the electron emissive coating 17, be of a thinness relative to the base member so as to result in no appreciable thermally caused mechanical distortion, or thermal bimetal effect, on the cathode as a whole. Now it is conceivable that under some circumstances it may not be possible or commercially expedient to construct a cathode in accordance with Fig. 2 of my" drawing in which the relative thicknesses of the base member 15 and the layer 16 are such that no appreciable bimetal effect or thermally caused mechanical distortion will result. For instance, it may well be that for certain combinations of material used in forming the cathode=it might prove difiicult to form the layer 16 to such a thinness, as to result in no-appreciable bimetallic etfect'when'se'curd to the base member, or from a standpoint of ease in fabrication of the cathode it may be desirable to form the layer 16 to a thickness at which some bimetal effect might result at high temperatures. In such cases bowing of the sides of the cathode structure due to a bimetal efiect may be avoided by coating both of the opposing surfaces of the base member 15 with the electron emissive substance base material.

In Fig. 3 is illustrated a cathode structure 13 modified in this manner. The cathode 13 shown in Fig. 3 is identical to that disclosed in Fig. 2 in that it includes a base member 15 formed of a low thermal expansion metal such as Invar, Nilvar, etc., an electron emissive coating of barium oxide, or the like, and an interposing layer of material 16 such as nickel, nickel alloy or any other material suitable for serving as a base for the emissive material. The cathode 13 shown in Fig. 3 difiers from that of Fig. 2 only in that it is modified to include a layer of material 18 suitably secured to the surface of the base member 15 opposite the layer 16. The layer 18 is similar to the layer 16 in expansion characteristics. Accordingly, any thermal bimetal effect that might tend to be caused by one of the layers of material 16 or 18 will be effectively opposed by the other with the result that such tendencies would be cancelled out and the wall of the base member 15 would remain substantially straight during operation of a tube incorporating the cathode.

It is to be understood that the layer 18 need be similar to the layer 16 in expansion characteristics only. This I accomplish by making both layers of the same material and thickness. However, the material of the layer 18 and the thickness of this layer could be different from that of the layer 16 while still having the same expansion characteristics and thereby being etfective for opposing any bimetal effect that might tend to be caused by the layer 16 in cooperation with the base member 15.

It is to be understood further that the layers 16 and 18 may be applied to the surfaces of the base members 15 in various ways. For example, they could be bonded by rolling or plating to the base member material when the latter is in sheet form and before the base members are formed. The layers could be plated on the base members after they are formed. Or the layers 16 and 18 could be formed as thin sleeves and slipped over or inserted into pre-formed cathode base sleeves and thereafter suitably secured to the base sleeves.

Thus, it will be seen that I have provided a new and improved electronic tube including a low expansion cathode structure adapted for being tightly fitted in support members and for retaining such fit during operation of the life of the tube for the purpose of minimizing microphonics. Further, my cathode structure includes a surface portion formedtof a material suitable for serving as a base for an electron emissive material coating, which surface portion has no adverse efiects on the fitting of the cathode in the supports therefor or on the spacing between the cathode walls and other elements of a tube cage. Still further, my structure is formed of a material having substantially low thermal conductivity whereby heat loss to the cathode supports is minimized for thereby minimizing axial cathode temperature gradients and increasing the thermal efiiciency of the structure. Additionally, the materials which I utilizein forming the base member of my structure include the desirable property of high strength at elevated temperatures.

While I have shown anddescribed specific embodiments of my invention, I do not desire my invention to be limited to the particular forms shown and described, and I intend by the appended claims to cover all modifications within the spirit'and scope of my invention.

What I claim as new and desire to secure by Letters Patentof the United States is:

1. A low-microphonic's electronic tube comprising; an envelope, electrode elements in said envelope, supporting means in said envelope for said electrodeelements, said electrode elements includingat least an anode and an indirectly heated cathode substantially consistently spaced throughout the lengths thereof, said cathode being subject to relatively wide temperature ranges during normal operation of said tube, said cathode being tightly fitted in said supporting means and comprising a low thermal expansion tubular base member, an electron emissive coating on said base member, and 'a layer of base material for said electron emissive coating interposed between said base member and said coating and secured to' a surface of said base member, whereby the tight fit between said cathode and supporting means and a substantially consistent spacing between said emissive coating and said anode substantially throughout the lengths thereof are maintained during said normal operation of said tube.

2. An electronic tube adapted for low microphon-ics and increased operating efficiency comprising; an envelope, electrode elements in said envelope, supporting means in said envelope for said electron elements, said electrode elements including at least an anode and an indirectly heated cathode substantially consistently spaced throughout the lengths thereof, said cathode being subject to relatively wide temperature ranges during normal operation of said tube, said cathode being tightly fitted in apertures in said supporting means and com prising a low thermal expansion and conductivity tubular base member, an electron emissive coating on said base member and a layer of base material for said electron emissive coating comprising nickel interposed between said base member and said coating and secured to a surface of said base member, said layer being thin relative to said member, thereby to minimize any thermally caused mechanical distortion of said cathode, whereby the tight fit in said apertures and a substantially consistent spacing between said emissive coating and said anode substantially throughout the lengths thereof are maintained and heat loss to said supporting means is minimized during said normal operation of said tube.

3. A cathode structure comprising; a member formed of a low thermal expansion sheet material, an electron emissive coating on said member, and a layer of base material for said electron emissive coating interposed between said member and said emissive coating and secured to a surface of said member, said layer being thin relative to said member, thereby to minimize any thermally caused mechanical distortion of said structure.

4. An indirectly heated cathode structure comprising; a heating element, a tubular base member containing said heating element formed of a low thermal expansion material and containing said heating element, an electron emissive coating on said base member, and a layer of "7 base material for said electron emissial coating interposed between said member and said coating and secured to a surface of said. member, the thickness of said layer relative to that of said member: being less than one to six, thereby to minimize any thermally caused mechanical distortion of said structure.

'5. Av cathode structure comprising; a member formed of a low thermal expansion sheet material, an electron emissive coating on said member, a layer of base material being thin relative to said member and for said electron emissive coating interposed between said member and said emissive coating and secured to a surface of said member, and another layer of material similar in thickness and expansion characteristics to said first-mentioned layer provided on the opposite surface of said member thereby to compensate for any thermally caused mechanical distortion thatmight tend to result in said structure from said member and said first-mentioned layer.

6. A cathode structure comprising; a member formed of a low thermal expansion sheet material, an electron emissive coating on said member, a base for said coating comprising nickel interposed between said member and said coating and secured to a surface of said member, and said base being thin relative to said member for minimizing any tendencytoward thermally caused mechanical distortion of said structure.

7.'A cathode structure comprising; a member formed of a low thermal expansion sheet material, an electron emissive coating on said member, and a base for said coating comprising a layer of nickel alloy interposed between said memberand said coating and secured-to a surface of said member, said layer of nickel alloy being thin relative to said member, thereby' to minimize any thermally caused mechanical distortion of said structure.

8 8. A cathode structure comprising; 'a member formed of a-low thermal expansion sheet material, an electron emissive coating on said member, and a base for said coating comprising a layer of nickel interposed between saidmember and said coatingand secured to a surface of said member, the thickness of said layer relative to said member being less than one to six thereby to minimize any thermally caused mechanical distortion of said structure.

9. An indirectly heated cathode structure comprising;

a heating element, a tubular member containing said heating element and formed of a low thermal expansion and low thermal conductivity material, a sleeve formed of a base material for said electron emissive coating fitted securely over said tubular member, an electron emissive coating provided on said sleeve, and another sleeve similar in expansion characteristics to said first-mentioned sleeve securely fitted in said tubular member, thereby to compensate for any thermally caused mechanical distortion that might tend to result in said structure from said tubular member and first-mentioned sleeve.

References Cited in the file of this patent UNITED STATES PATENTS 

